Thermostatic mixing valve (TMV) cartridges are readily available in the plumbing industry. They are inserted in form fitting housings and are usually mounted to a vertical wall in a shower area. Although quite reliable, these valves have adjustments known as ring stops which set the maximum rotation in both the hot and cold setting directions. The adjustments permit accommodation for the supply temperatures and pressures of the hot and cold water supplies. Besides an initial adjustment at installation, any changes that effect the temperature and pressure of the water supplies may call for readjustment. These changes include plumbing changes, seasonal temperature changes, change of a domestic hot water appliance, addition or removal or cleaning of line filters, or even customer preference. These adjustments are accessible from the valve temperature adjustment end on the user side of the vertical wall by simply removing a handle and a cap. This is possible due to the limited predictable thickness of the vertical wall which typically are made of sheet rock with a mastic layer followed by grouted tile. The ring stops can be simply pulled off a fluted shaft and reinstalled in a different position by using one's fingers.
When installing a thermostatic mixing valve (TMV) for a hand held shower or other faucet on a horizontal deck, there are two problems that are not encountered on vertical wall installations. One relates to the wide variation in substrate thickness that can be encountered due to the variety of materials used. Another limitation is the narrow bathtub edge if this is, in fact, the horizontal deck intended for installation. Custom solutions have included installation kits which require large deck openings to permit topside access to thermostatic mixing valve (TMV)'s. Other attempts have used special tools to reach the ring stops installed on thermostatic mixing valve (TMV)'s which are a distance below the deck surface.
There is not a universal thermostatic mixing valve (TMV) which will accommodate a wide variety of deck thicknesses, permit easy hand reachable ring stop adjustment, and is easily installed through a single round hole in even a narrow deck area.